Double-layer-structured catalyst for dehydrogenating light hydrocarbons

ABSTRACT

A double-layer structured catalyst for use in dehydrogenation of light hydrocarbon gas within a range of C3 to C6, configured such that platinum, tin, and an alkali metal are carried in a phase-changed carrier, wherein the tin component is present in an entire region inside the carrier, and the platinum and the tin form a single complex and are present in an alloy form within a range of a predetermined thickness from an outer periphery of the carrier.

TECHNICAL FIELD

The present disclosure relates to a double-layer structured catalyst fordehydrogenating light hydrocarbons and a method of manufacturing thesame. More particularly, the present disclosure relates to a technologyof a catalyst and a manufacturing method of the catalyst, in which thecatalyst contains two kinds of metal components in an alloy form presentwithin a range of a predetermined thickness on a surface of a catalystcarrier and one of the two kinds of metal components is distributed inan entire region of the catalyst, and the catalyst has high durabilityand high regeneration efficiency when used in dehydrogenation of lighthydrocarbons.

BACKGROUND ART

A dehydrogenation of light hydrocarbons using a catalyst has advantagesin that a product having a high yield and a high purity is obtained, andis a reaction having a high manufacturing efficiency and simple process.Therefore, research related to the manufacture of light olefins bydehydrogenation using a catalyst has been ongoing steadily.

The present applicant has disclosed a catalyst that exhibits improvedselectivity and reactivity, and is suitable for use in the manufactureof an olefin by dehydrogenating C3, C4, or C9 to C13 paraffin. Moreparticularly, a technology for manufacturing a catalyst configured suchthat a thermally treated carrier having controlled pores is used andmost metal components contained in the catalyst are uniformlydistributed not in the form of individual metals but in the form of analloy in the carrier from the outer periphery or in the entire region ofthe catalyst (Korean Patent Application Publication No. 10-2017-0054789,Published on May 18, 2017 and Korean Patent No. 10-176170, Published onMar. 14, 2017). In the related art of a dehydrogenation catalyst, foractive site control, since dehydrogenation intensity of platinum is toostrong, an alkali metal is introduced, and tin is introduced in aneffort to prevent deterioration of catalyst activity due to carbondeposition.

DISCLOSURE Technical Problem

According to the related art, there is a problem in that since acatalyst in which platinum and tin in the form of an alloy aredistributed partially within an outer surface portion or uniformlywithin an entire region of an alumina carrier is used, the catalystactivity is lowered due to a situation that a carbon coke deposited inthe alumina carrier covers an active site, and even when the coke isremoved from the carrier by using a calcination process, it is almostimpossible to completely regenerate the catalyst into an initial statedue to the coke which remains therein.

Technical Solution

In order to achieve the above objectives, according to one aspect of thepresent disclosure, there is provided a double-layer structured catalystfor use in dehydrogenation of light hydrocarbon gas within a range of C3to C6, configured such that platinum, tin, and an alkali metal which arecarried in a phase-changed carrier, and the tin component is present inan entire region inside the carrier, and the platinum and the tin form asingle complex and are present within a range of a predeterminedthickness from an outer periphery of the carrier.

In another embodiment of the present disclosure, the single complex ofplatinum and tin is formed within a range of a thickness of 300 to 500μm from the outer periphery of the carrier, and the carrier may beselected from the group consisting of alumina, silica, zeolite, and acomplex component thereof.

In the present disclosure, a catalyst for dehydrogenating a lightparaffinic hydrocarbon has actually the same aspect as that of therelated art in that an alloy of platinum and tin in the carrier arepresent within a range of a predetermined thickness from the surface ofthe carrier to the inner core. However, it should be noted that unlikethe related art, the tin component in the catalyst of the presentdisclosure is uniformly distributed in the inner core. This newdouble-layer structure induces a coke to be formed extensively insidethe carrier rather than only the dehydrogenation active site, and thusincreases durability and also minimizes aging due to a coke oxidation sothat a catalyst that inhibits the sintering of active metals may beprovided.

An objective of the present disclosure is to improve efficiency ofactivation and regeneration by the influence of the coke by placingcoke-inducing material in the center of the carrier in contrast to therelated art which does not have an active metal in the inner core of thecarrier.

Advantageous Effects

In the catalyst having the double-layer structure according to thepresent disclosure, the tin component is uniformly present in the coreof the carrier, while the platinum and the tin in the form of an alloyare distributed within a range of a predetermined thickness inside thecarrier. Here, the tin component distributed to the center or to thecore of the carrier spreads the coke generation not only onto the activesite of the alloy of platinum and tin but also into the inside of thecarrier, thus minimizing the inactive phenomenon of the platinum causedby the coke generation, and increasing the durability of the catalyst,while reducing the formation of the coke on the active site, so that theaging of the catalyst is reduced and the sintering of the platinum isprevented, whereby the improved regeneration of the catalyst isrealized.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view schematically illustrating a structural difference of acatalyst that has been improved from a conventional technology to adouble-layer structured catalyst of the present disclosure;

FIG. 2 is a flowchart illustrating a manufacturing process of thedouble-layer catalyst of the present disclosure;

FIG. 3 illustrates electron probe microanalysis (EPMA) images comparinga catalyst of the conventional technology (a) with a double-layerstructured catalyst of the present disclosure (b);

FIG. 4 illustrates electron microscope images (video microscopy)comparing a state of a catalyst of the conventional technology with thedouble-layer structured catalyst of the present disclosure beforeregeneration.

BEST MODE

The present disclosure relates to a double-layer structured catalyst fordehydrogenating light hydrocarbons and a method of manufacturing thesame. More particularly, the present disclosure relates to a catalystand manufacturing of method of the catalyst, in which the catalystcontains two kinds of metal components, for example, platinum and tin inan alloy form are present within a range of a predetermined thickness ona surface of the carrier, and one of the two kinds of metal components,for example, the tin is distributed within an entire region of thecatalyst, whereby the catalyst is improved in durability andregeneration efficiency when used in dehydrogenation of lighthydrocarbons since the coke generation is distributed to the entireregion of the carrier.

From the conventional technology, it has been noted that when the activemetals of the dehydrogenation catalyst of light paraffinic hydrocarbonsare not distributed alone in the carrier but the active metals in analloy form are present within a range of a predetermined thickness fromthe surface of the catalyst to the inside thereof, it is possible tomanufacture a catalyst capable of greatly increasing the conversion rateof paraffin, olefin selectivity, and durability. However, problems stillremain due to coke.

In the present disclosure, the active metal of the catalyst refers toplatinum, but comprehensively includes tin, and the double-layer refersto a structure wherein the inside of the carrier is divided into twolayers. For example, the alloy of the platinum and tin is present in theouter layer, and the tin component is placed in the inner layer. Theterm ‘double-layer’ contrasts with a structure of the conventionaltechnology which did not have any active component in the inner core. Inthe present disclosure, the term ‘alloy’ may be used interchangeablywith the term ‘complex’. The inner layer of the carrier may be referredto as the ‘core’, ‘egg’, or ‘center’, and the outer layer of the carriermay be referred to as the ‘shell’. An outer layer thickness or a coredepth may vary depending on the alloy depth. In other words, thethickness or the depth of the outer and inner layers may vary dependingon the alloy depth and is not fixed. In the present disclosure, thecarrier may be selected from the group of consisting of alumina, silica,zeolite, and a complex component thereof. In addition, the lighthydrocarbon gas refers to light paraffin. More particularly, the lighthydrocarbon gas is straight chain-type or branch-type hydrocarbons in arange of C3 to C6. The catalyst for dehydrogenation of lighthydrocarbons is subjected to a relatively high-temperature reactioncompared to heavy hydrocarbons, thus forming a large amount of coke dueto thermal decomposition and other side reactions. However,surprisingly, the problem of the coke was solved by placing the tincomponent in the core of the dehydrogenation catalyst carrier of therelated art. Specifically, the tin component placed up to the center ofthe carrier spreads coke generation not only to the active sites ofalloy of platinum and tin but also to the inside of the carrier, thusimproving the durability of the catalyst by minimizing a coveringphenomenon of the platinum. Moreover, by minimizing the generation ofthe coke on the active sites, the sintering phenomenon of the platinumwas prevented by reducing aging during the regeneration process, therebyrealizing improved regeneration efficiency of the catalyst. In otherwords, the coke density in the active component alloy is decreased.

In the present disclosure, a process of carrying the tin of uniformdistribution on the core of the carrier is performed before carrying anactive metal alloy complex, and the platinum and tin are formed into thecomplex within an organic solvent and are simultaneously carried with acertain amount of inorganic acids and/or a certain amount of organicacids, and distributing them within a range of a predetermined thicknesson the surface of the carrier is performed to complete the catalystmanufacture.

FIG. 1 is a view schematically illustrating a structural difference of acatalyst that has been improved from a conventional technology to adouble-layer structured catalyst of the present disclosure. In adehydrogenation catalyst of the conventional technology, platinum andtin form a single complex and are present within a range of apredetermined thickness from the outer periphery of the carrier. Forexample, platinum and tin are present in the shell as an alloy, whereasthe dehydrogenation catalyst of the present disclosure has a shell-eggstructure with an evenly added tin component in the core of the carrier.

FIG. 2 is a flowchart illustrating a manufacturing process of thedouble-layer catalyst of the present disclosure, which comprehensivelyexplains the method of the present disclosure.

1) Pre-Treatment Process with the Tin Precursor Solution

In order to increase the pore size and the pore volume, the carrier isheat-treated in a calcination furnace at 1000 to 1050° C. for 1 to 5hours, whereby gamma alumina is phase-changed to theta alumina prior tousing the carrier. During the manufacture of the tin precursor, acertain amount of the tin precursor is mixed with an excessive amount ofinorganic acid such as hydrochloric acid and nitric acid, and placed themixture in deionized water, where the excessive amount of the inorganicacid acts as a double role that makes the melting of the tin precursorsin the deionized water easy and ensures that the tin precursor reachesthe core portion of the carrier. The carrier is placed in the producedtin precursor solution until that the carrier is completely submerged,and the carrier is aged for 2 to 24 hours to allow the tin component toreach the core of the carrier, and then a filtering process is performedto remove moisture therefrom primarily. Thereafter, a drying process isperformed at 80 to 150° C. for 24 hours, thus secondarily and completelyremoving moisture remaining in the catalyst, and then a calcinationprocess is performed at 400 to 700° C. in air, thus obtaining apre-treated catalytic structure in which tin is placed in the entireregion thereof.

2) Process of Manufacturing Stabilized Platinum-Tin Composite Solution

The composite solution of platinum and tin readily causes precipitationof platinum in air due to the high reducibility of tin. Therefore,selection of a solvent is very important in the manufacture of thecomposite solution. First, the precursors of platinum and tin were addedto the organic solvent so that the platinum-tin composite was notdecomposed when being mixed with each other, and hydrochloric acid wasadded to manufacture an acidic solution. Then, an organic acid was addedto the organic solvent in order to increase the penetration speed intothe inside of the carrier. During the manufacture of the platinum-tincomposite solution, the solution is kept in an inert gas atmosphere anddecomposition by oxygen is suppressed whereby stabilization of thesolution is achieved. Here, nitrogen, argon, and helium may be used asthe inert gas, and nitrogen gas is preferably used.

3) Process of Manufacturing Double-Layer Structured Catalyst UsingStabilized Platinum-Tin Composite Solution and Alkali Metal

In the process of carrying the active metal alloy solution, aplatinum-tin composite solution is manufactured in an amount ofequivalent to the total pore volume of the carrier, and is impregnatedin the carrier using a spray-carrying method. After the impregnation, anaging process is performed for a predetermined period of time in orderto control the penetration depth of platinum and tin into alumina by anorganic acid. After the aging process, a rapid drying process isperformed while fluidizing the catalyst in an atmosphere of 150 to 250°C., thus removing most of the organic solvent remaining in the catalyst.Water remaining in the catalyst is completely removed via a dryingprocess at 100 to 150° C. for 24 hours. The reason for performing rapiddrying is to prevent the platinum-tin composite solution from diffusinginto the carrier together with an inorganic or organic acid solvent overtime when the platinum-tin composite solution is carried in the aluminacarrier in which the tin component is already placed. After drying, anorganic material is removed under a nitrogen atmosphere at 250 to 400°C., followed by a calcination process in an ambient atmosphere at 400 to700°.

After calcination, a process for carrying alkali metal is performed inorder to suppress the catalyst side reaction. First, potassium iscarried in the internal pores of the carrier using the samespray-carrying method as in the process of manufacturing theplatinum-tin composite solution, and a drying process at 100 to 150° C.for 24 hours, and a calcination process in an ambient atmosphere at atemperature within a range of 400 to 700° C. are performed. Finally,after the calcination, a reduction process is performed using ahydrogen/nitrogen mixed gas (a range of 4%/96% to 100%/0%) at atemperature within a range of 400 to 600° C., thus obtaining a finalcatalyst.

The electron probe microanalysis (EPMA) images of the double-layercatalyst manufactured by the method are shown in FIG. 3b . FIG. 3aillustrates an electron probe microanalysis (EPMA) image of a catalystof the conventional technology, and FIG. 3b illustrates an electronprobe microanalysis (EPMA) image of a double-layer structured catalystof the present disclosure. The core of the carrier of the presentdisclosure has a uniformly distributed tin component, whereas there isno active metal component in the core of the carrier in the conventionaltechnology.

After packing the double-layer structured catalyst manufactured by themethod of the present disclosure to a fixed-bed catalytic reactor, andthen generating an olefin by the dehydrogenation reaction, whether acoat forms or not inside the catalyst is observed. FIG. 4 illustrateselectron microscope images (video microscopy) comparing a state of acatalyst of the conventional technology with the double-layer catalystof the present disclosure before regeneration. A coke deposition isobserved in the core of the double-layer catalyst of the presentdisclosure as expected, while the coke formation is suppressed in thecatalyst of the conventional technology. Therefore, the coke density atthe catalyst active site is significantly lower for the double-layercatalyst of the present disclosure, resulting in a substantial increasein durability and regeneration efficiency of the catalyst of the presentdisclosure.

1. A double-layer structured catalyst for use in dehydrogenation oflight hydrocarbon gas within a range of C₃ to C₆, the catalystcomprising: platinum, tin, and an alkali metal which are carried in aphase-changed carrier, wherein the tin component is present in an entireregion inside the carrier, and the platinum and the tin form a singlecomplex and are present in an alloy form within a range of apredetermined thickness from an outer periphery of the carrier.
 2. Thecatalyst according to claim 1, wherein the predetermined thickness fromthe outer periphery of the carrier is 300 to 500 μm thick.
 3. Thecatalyst according to claim 1, wherein the alkali metal is selected fromthe group consisting of potassium, sodium, and lithium.
 4. The catalystaccording to claim 1, wherein the carrier is selected from the groupconsisting of alumina, silica, zeolite, and a complex component thereof.